The present invention relates generally to semiconductor fabrication and, more particularly, to a system and method for controlling byproduct build-up on a polishing pad in, e.g., a linear chemical mechanical planarization (CMP) system.
In the fabrication of semiconductor devices, CMP is used to planarize globally the surface of an entire semiconductor wafer. CMP is often used to planarize dielectric layers as well as metallization layers. As is well known to those skilled in the art, metallization layers are formed of conducting metals, e.g., aluminum and copper. During the CMP of copper films, CuxOy byproducts are formed and the surface of the polishing pad absorbs these byproducts. The build-up of CuxOy byproducts on the pad surface increases with each passing wafer. This is problematic because these byproducts introduce additional abrasivity into the CMP process. The additional abrasivity introduced by the CuxOy byproducts is undesirable because it affects removal rate uniformity and leads to process instability and lack of control. In addition, byproduct build-up in the grooves formed in the pad can impede slurry transport. When slurry transport is impeded, control of the within-wafer nonuniformity and the removal across the wafer may be lost.
To ensure wafer-to-wafer process repeatability and control, the build-up of CuxOy byproducts should be removed from the polishing pad. One way to remove these byproducts is to introduce and distribute an appropriate chemistry across the pad surface. The chemistry will react with the CuxOy byproducts and convert or complex them into ionic form so that they can be rinsed from the surface of the polishing pad. In the past, chemistries have been dripped onto the surface of the polishing pad. This technique suffers from two potential drawbacks, however. First, the overall process productivity may be adversely impacted because of the time interval required to remove thoroughly all of the byproduct materials. Second, prolonged exposure to the chemistry can compromise the passivation film that protects the low-lying regions of copper. If this passivation film is compromised, then wet etching can occur in the low-lying regions of copper. Such wet etching is undesirable because it causes the planarization efficiency of the process to fall off significantly and leads to increased dishing and erosion problems.
In view of the foregoing, there is a need for a method that efficiently removes byproduct build-up from a polishing pad in a linear CMP system without adversely impacting the overall process productivity or the planarization efficiency.